Lab 7

class DNS{
        String host;
        String IPAddr;
        DNS(String host,String IP){

                this.host=host;
                this.IPAddr=IP;
        }
}
class DNSHashTable{
        ArrayList<DNS> table[]; //An array of ArrayList of DNS objects
        DNSHashTable(){
        table = new ArrayList[53];
        for(int i = 0; i < table.length; i++)
                table[i] = new ArrayList<DNS>();
        }
        public static long compmap(long key){
                return key%53L;
        }
        public static long hashcodemap(String host){
                char[] data = host.toCharArray();
                long value = 0;
                int a = 33;
                int len = data.length;
                for(int i=0;i<len;i++){
                        char ltr=data[(len-1)-i];
                        if(Character.isLetter(ltr)){
                                value *=a;
                                value +=(int)ltr; //Going backwards
                        }
                }
                return value;
        }
        public void insert(DNS dns){
                int index = (int)compmap(hashcodemap(dns.host));
                table[index].add(dns); //Avoids Colision using Seperate Chaining
        }
        public void Find(String hostname){
                System.out.println();
                int index = (int)compmap(hashcodemap(hostname));
                System.out.println(hostname+" May be found at table index : "+index);
                if(table[index]==null){
                        System.out.println(hostname+" Index not in mapping");
                        return;
                }
                ArrayList<DNS> List = table[index];
                for(int i=0;i<List.size();i++){

                        if(List.get(i).host.compareTo(hostname)==0){
                                System.out.println("IP Address of "+hostname+" is : "+List.get(i).IPAddr);
                                return;
                        }
                }
                System.out.println(hostname+" Not found in mapping index");
        }
        public static void main(String[] args) {
                DNSHashTable map= new DNSHashTable();
                map.insert(new DNS("google.com","172.217.11.174"));
                map.insert(new DNS("bbc.co.uk","212.58.241.131"));
                map.Find("google.com");
                map.Find("bbc.co.uk");
                map.Find("youtube.com");
        }